Hearing devices are wearable hearing apparatuses which assist hard-of-hearing people. In order to accommodate numerous individual requirements, various types of hearing devices are available such as behind-the-ear (BTE hearing devices, in-the-ear hearing devices (ITE), conch hearing devices, and so on. The hearing devices listed as examples are worn on the outer ear or in the auditory canal. Bone conduction hearing aids, implantable or vibro-tactile hearing aids are also available on the market. The damaged ear is thus stimulated either mechanically or electrically.
The key components of hearing devices are principally an input converter, an amplifier and an output converter. The input converter is normally a sound receiver e.g. a microphone and/or an electromagnetic receiver, e.g. an induction loop. The output converter is most frequently realized as an electroacoustic converter e.g. a miniature loudspeaker, or as an electromechanical converter e.g. a bone conduction hearing aid. The amplifier is usually integrated into a signal processing unit. This basic configuration is illustrated in FIG. 1 using the example of a behind-the-ear hearing device. One or a plurality of microphones 2 for recording sound from the environment are built into a hearing device housing 1 to be worn behind the ear. A signal processing unit 3 which is also integrated into the hearing device housing 1 processes and amplifies the microphone signals. The output signal for the signal processing unit 3 is transmitted to a loudspeaker or earpiece 4, which outputs an acoustic signal. Sound is transmitted through a sound tube, which is fixed in the auditory canal by means of an otoplastic, to the device wearer's eardrum. Power for the hearing device and in particular for the signal processing unit 3 is supplied by means of a battery 5 which is also integrated in the hearing device housing 1.
Modern hearing devices normally feature a plurality of input channels. Input channels can be provided among other things through a microphone, a telephone loop, a directional microphone, an audio shoe and a digital input. Further additional input channels are expected to be added in future, for example for Bluetooth, wireless communication between hearing devices, etc. The optimum input channel depends in each case on the particular situation. If for example an induction loop is available in the vicinity of the hearing device wearer, the telephone loop would be the optimum input channel to select in this case.
To date the particular input channel has mostly had to be set manually. This frequently represents a major problem especially for older and very young hearing device wearers. A special mechanical solution, in which an audio shoe is attached to the hearing device, represents an improvement in this situation. Once the audio shoe has been attached, it is also selected as an input channel. A further example of automation is represented by the automatic activation of a telephone loop with the aid of a reed relay as soon as a magnetic near field from the telephone acts on the reed relay.
The publication EP 1 484 942 A2 further describes an automatic switchover between a telephone loop and a microphone with the aid of a signal classification. Patent specification EP 0 989 775 B1 further discloses a hearing device with a system for signal-quality monitoring. The monitoring system determines signal quality for the respective audio signal for example by means of a comparison with a specific reference value for the corresponding audio signal. The option is also specified to insert an identifier into the artificially-generated e.g. inductive, infrared or radio signals, which can be recorded by the monitoring system with little technical outlay and which indicates that the corresponding signal is of adequate quality. In each case signal quality is thereby determined from the signal itself. In principle this represents a solution to the problem described above, but problems arise for example when the telephone loop is being used when telephoning and loud background noise is introduced by means of the microphones, and it is only possible to determine whether the signal is a useful signal by means of the level on the corresponding channel.
The publication DE 102 11 364 A1 further describes the deactivation of signal processing devices of a hearing device. In order to reduce power consumption the hearing device is equipped with an internal or external hearing device signal source with a signal line for transferring a signal to a hearing device amplifier and a control system for activating and deactivating the hearing device signal source. A monitoring logic monitors the signal line and supplies a switching signal to the control system so that the hearing device signal source can be activated and deactivated on the basis of the switching signal. Self-deactivation is achieved through a reduction in the load impedance.
The publication EP 0 219 025 B1 further discloses a hearing device with a sound-recording microphone arrangement and an earpiece between which is inserted an arrangement comprising a plurality of voice frequency selector channels, which enables only the strongest channels in a multi-channel system to have an effect through continuous and reciprocal influencing of control signals of neighboring channels. The weaker channels are then completely suppressed. For this purpose an inhibition circuit is provided by means of which strong channels are emphasized and weaker channels are suppressed, taking account of signal strengths in neighboring channels.
The publication DE 10 2004 013 952 A1 further discloses a circuit arrangement having a plurality of filter stages of a filter bank and a plurality of resonator circuits. The circuit arrangement also contains a resonator control circuit for controlling or regulating the rating of the resonator circuits. Each of three resonator circuits are connected in series along a respective channel of the matrix-type arrangement such that a respective output of an upstream resonator circuit is connected with a respective input of a downstream resonator circuit. The resonator control circuit is connected communicatively with all resonator circuits. The rating of each individual resonator circuit is adjustable by means of the control circuit with the control circuit being configured such that it adjusts the rating of the resonator circuits as a function of the amplitude of an output signal of the last resonator circuit in a certain channel.